Nowadays, infrastructure projects seem to become more complex and the project manager’s ability to control projects decreases. Therefore, it is crucial to adapt project management to cope with the emerging complexity. Flexibility options are explored to deal with the increasing complexity. To grasp complexity, a selection of the Technical, Organisational and External framework was used. Eleven flexibility enablers are studied to operationalise them and make them applicable for project managers. In this explanatory research, a case study has been done to explain the possibilities for flexibility enablers to cope with the found complexities. The results of the individual case study and the cross-case study provided input for a proposal on how flexibility enablers facilitate the management of project complexity. A selection of related complexity elements and flexibility enablers have been used to develop a flexible project management tool. The tool provides insights into the selected complexities, creates awareness on flexibility perspectives from the project team, allows to choose the operationalised flexibility enablers, and reflects on the changes made to keep improving. The tool is meant to be used throughout the project and supports incorporating flexibility to be a dynamic process. Concluding, the awareness of complexity and flexibility helps to cope with complex infrastructure projects. The developed tool for project management will help apply specific flexibility enablers to cope with relevant complexity elements. Future research into other construction organisations is needed to generalise the findings of the operationalisation of the selected flexibility enablers. Also, future research is recommended on the awareness and the adaptation possibilities for flexibility in project management within the infrastructure.